In factories, a process of heating a metal plate or the like is one important working process. There are various methods of such heating, one of which is an induction heating method. Basically, in the induction heating method, alternating current is supplied to a coil to generate magnetic flux which is introduced to a heating object, such as a metal plate, to generate induction current in the heating object to thereby heat the heating object.
In such an induction heating apparatus, magnetic flux hardly passes through a center portion in a width direction of a heating object (i.e., an object being heated), while easily passing through edge portions of the object. Therefore, magnetic flux that flows from the center portion, circulating around the edge portions, is increased in a magnetic flux distribution and thus the magnetic flux is concentrated on the edge portions to raise magnetic flux density there. As a result, the edge portions tend to be excessively heated, which leads to difficulty in ensuring uniformity in temperature distribution between the edge portions and the center portion (hereinafter is referred to as “heat uniformity”).
When a heating object is a thin plate, in particular, a transverse method is generally used, in which magnetic flux is introduced to the heating object in a direction perpendicular to the object. In this case, the edge portions are overheated and thus the heat uniformity is unlikely to be ensured. In this regard, in the induction heating apparatus based on a transverse method disclosed in Patent Literature 1, magnetic members are arranged near edge portions of a heating object so that magnetic flux is collectively passed through the magnetic members to suppress overheating of the edge portions.